palliation vs alleviation

palliation and alleviation both are nouns.

Word	Noun	Adjective	Verb	Adverb
palliation	Yes	No	No	No
alleviation	Yes	No	No	No

As nouns, alleviation is a hypernym of palliation; that is, alleviation is a word with a broader meaning than palliation:

palliation: easing the severity of a pain or a disease without removing the cause
alleviation: the act of reducing something unpleasant (as pain or annoyance)

Other hypernyms of palliation include easement, easing, relief.

palliation (noun)	alleviation (noun)
easing the severity of a pain or a disease without removing the cause	the act of reducing something unpleasant (as pain or annoyance)
to act in such a way as to cause an offense to seem less serious	the feeling that comes when something burdensome is removed or reduced